The present invention relates to apparatus for selectively transmitting fluids. More particularly, the invention relates to methods and apparatus for transferring minute quantities of a plurality of fluids to a single mixing chamber. Yet more particularly, the invention is directed to methods and apparatus for preventing inadvertent transfer of a fluid wherein a line for transmitting the fluid is occluded.
A variety of devices and/or applications are designed such that one or more fluids are selectively conducted from individual sources to one or more common receptacles. One example of a device including such a feature is disclosed in U.S. Pat. No. 4,789,014, the teachings of which are fully incorporated herein.
In the device disclosed in U.S. Pat. No. 4,789,014, fluids such as drugs, are conducted from source vials to a common mixing and weighing chamber. The mixed fluids are then conducted to a single receptacle such as a bag of an administration set.
It is disclosed that the fluids added to the mixing chamber can be of very minute quantities--on the order of a few drops. As such, it is apparent that even minute quantities of the fluids can be significant. Accordingly, it is important to ensure that even minute quantities of fluids are not added to the mixing chamber.
As is further disclosed in U.S. Pat. No. 4,784,014, commencing at column 7, line 55, each tube that couples a respective vial to the mixing chamber is connected to a manifold in the upper portion of the chamber. The manifold includes a series of connector conduits to which one end of each of the individual tubes can be attached to provide fluid communication between the individual fluid tubes and the chamber when the manifold is connected to the chamber. The manifold includes individual spaced-apart, drop-former structures for each line for discouraging accumulation of droplets on the manifold. This prevents possible mixing of incompatible solutions due to droplets hanging on the manifold.
Positioned upstream of the manifold is a unit containing individual occlusion devices, one occlusion device for each tube coupled to a source fluid vial. The occlusion devices are employed to selectively occlude their respective tubes to allow fluid to flow from their respective source vial to the chamber.
To assist in the transfer of a fluid from a source vial, it is disclosed that the mixing and weighing chamber is placed under a vacuum pressure to thereby create vacuum assisted transfer. One problem that can arise in such a situation, however, is that such a vacuum in the chamber will also exert a vacuum pressure on all of the drop former outlets. Should an occluded tube contain a bubble/small volume of air between the occlusion device and the chamber, it is possible for the vacuum pressure to create an expansion of that bubble in the tube downstream of the occlusion device. Essentially, expansion of the air can cause displacement of fluid downstream of the bubble, this possibly causing fluid to drop from the drop former into the measuring chamber despite the fact that the particular tube is in an occluded state. Accordingly, fluid can be transferred although its particular tube might be perceived to be occluded.
As a result of the foregoing, it is possible that erroneous measurements of transferred fluids can be made. Further, it is possible that undesirable dosages of fluids can be added to a mixture.